​My Inspiration

​I came across this great book from 1938 on how to build four different short wave receivers. What was even cooler is that someone took the time to format it in Kindle EBook format! One click and a Kindle version of the vintage "HOW TO BUILD 4 DOERLE SHORT WAVE SETS" book was mine!

"HOW TO BUILD 4 DOERLE SHORT WAVE SETS" Kindle book on Amazon!

What is a Doerle Short Wave Set?

Doerle "sets" were a popular home built regenerative shortwave receivers of the 1930s. Designed by amateur radio enthusiast Walter C. Doerle of Oakland, California. Doerle's regenerative radio designs were published in many amateur radio magazines in the 1930s. Doerle's Short Wave Set designs were so popular in the 1930s because of the ease of construction and use of inexpensive parts in their design.

Not much is know about Walter C. Doerle or if he was even compensated for the designs featured in the book "How to build 4 Doerle Short Wave Sets" and other vintage publications.

The Doerle name lives on as his shortwave set designs are still popular with "Glowbug", amateur radio enthusiasts that enjoy building simple tube radios, of today.

Can I still purchase vacuum tubes?

Absolutely, there are many vendors that sell vacuum tubes and high voltage electronic components required for vacuum tube circuits. Many musicians and audiophiles even today love the sound of vacuum tube audio amplifiers as they believe they produce a warmer more natural sound. As such, there are many vendors that cater to their vacuum tube needs.

The type 30 and 32 vacuum tubes, and other components used in this shortwave receiver, are available from the two vendors below.​

​Source of Vacuum Tubes and related components

Building a Doerle "Signal Gripper" Regenerative Shortwave Receiver

Step 1 Source Vacuum Tubes and Electronic Parts

I found everything required to build my Two Tube Doerle Shortwave Radio set from Antique Electronic Supply (AES), the link to this company's web site was provided earlier. ​

My Eico 635 Tube Tester doesn't have the ability to test vintage Type 30 and Type 32 vacuum tubes. So I test them by placing them in an actual circuit. Pictured below is an earlier one tube regenerative receiver I built with Type 30 vacuum tube, to be tested, installed.

​Step 2 Design and Build Cabinent

The cabinet is made of salvaged wood from shelves that used to hang in my garage. I used degreaser to remove motor oil from the surface. Once degreased and dry, I used a palm sander to smooth out dents and imperfections.

​The cabinet for my shortwave receiver is going to be open type. Basically, L shaped with the top piece used as the front panel with all of the controls, and a bottom where the majority of parts are to be installed.

The shafts for the Tuning, Detector, Regeneration, and Filament controls are not long enough to protrude through the front of the 3/4 inch wood. So I decided to carve out cylindrical areas in the wood so that the shafts could protrude through the front. The first step was to mark placement.

​Next, it was time to layout the parts on the bottom panel then check for fit and placement. I place paper under the parts and mark placement on the paper once I am satisfied with the layout.

Once I am satisfied with parts placement on the bottom panel. I transfer the drill hole positions from the paper layout to the wooden panel using a punch.

I then use a drill press to machine the bottom panel. The holes for the standoffs are drilled completely through the bottom panel. I set the drill press stop for all of the rest of the holes so that they are drilled to a uniform depth.

I use a Wooden Hole Saw Set to drill concentric holes 5/8 inch deep into the back of the front panel.

I then use a screwdriver, like a wood chisel, to remove the remaining wood between the concentric circles drilled by the Wooden Hole Saws.

​This is how the back of the front panel looks after the remaining wood was removed from the indentations created. The indentations were then sanded to remove any roughness.

I created a paper template of the bottom panel for parts placement and to plan out the wiring.

Time for two coats of polyurethane!

I lightly sand each panel between coats.

I glue aluminum foil, the same type you use to wrap food in, to the back of the front panel. Elmer's White Glue works fine. This foil will be tied to circuit ground in order to reduce the effects of hand capacitance during operation.

​Finally, some rubber feet on the back side of the bottom panel.

​"Old Time Radios! Restoration and Repair" book on Amazon

​I consult this book often during radio restoration. I grew up in the transistor and rectifier era and this book taught me a lot about vacuum tube and selium rectifier technology.

Step 3 Final Mounting of Electronic Parts

It is easiest to mount the variable capacitors, variable resistor, and ground wires to the front panel before attaching it to the bottom panel.

I also mount terminals and knobs then label the front panel before attaching to the bottom panel.

​​Finally, I mount the hardware on the bottom panel and apply labels. I then attach the bottom to the front panel.

​Step 4 Wiring

Creating a wiring diagram a head of time makes wiring easier!

Here is my receiver ready for wiring.

​First, I wired all of the ground connections (Black wires).

Followed by the tube filament circuit (Red wires).

Then the 45 Volt circuit (Yellow wires).

Next the 90 Volt circuit (Purple wires)

Green wires for the antenna and tank circuit.

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Step 5 Winding the Plug-In Coils

Three windings are required for this regenerative receiver, all wound on Bakelite tube bases. The number of turns required for each coil can be found in the "HOW TO BUILD 4 DOERLE SHORT WAVE SETS" book.
​
The tank circuit plug-in coil has a single winding while the regenerative/detector circuits plug-in coil has two separate windings.

We will need a total of six plug-in coils in order to cover the 15-25M, 24-45M, and 40-110M bands. Plug-in coils are plugged into tube sockets, using matching pairs, in order to change bands.

​The plug-in coil below is part of the tuned tank circuit, mounted on a four pin Bakelite tube base. I use 24 AWG enamel coated copper wire for all of the coils. Hot glue is used to secure the copper windings to the tube base.

A tiny drill is used to drill holes into the tube base so that the copper wires have entry points into the center of the tube base.

I scrap the enamel insulation from the ends of the wire using an X-Acto knife. I then solder the wires to the pins of the tube base.

Finally, I check each coil's continuity at the pins.

A label is inserted into each finished plug-in coil to indicate its reception bands.

​Here is an example of a finished regenerative/detector circuits plug-in coil. As you can see, two windings are wound on the tube base.

Below is an inside view of a finished regenerative/detector circuit plug-in coil. You can see the wires from each winding enter the center of the tube base through tiny drilled holes. The wires then enter the pins where they are soldered in place.

Pictured below are two sets of plug-in coils, one set is for the 24-45M and the other is for the 40-110M bands. I ran out of tube bases and will have to wind the 15-25M plug-in coil set some other time.

​Step 6 Final Prep

Install the two Type 30 Triode Tubes and the Type 32 Tetrode tube into the proper sockets, plug the matching band plug-in coils into the proper sockets.

​​Step 7 Obtain Suitable Power Supply

In my "Battery Box", I use two D batteries for the 2 Volt filament voltage. I connect many 9 Volts in series to obtain the 90 and 45 Volts needed to power the receiver.

Fahnestock Clips on the back of the "Battery Box" provide access to the required Voltages.

The next step is to connect your newly constructed receiver to a suitable power supply, antenna, and ground. I use my external G5RV Amateur Radio antenna and main water pipe that comes into our house as a ground. In addition, connect high a impedance earphone to the front.

Here is a front view showing the Tuning, Detector, Filament, and Regeneration controls. In addition, connections for headphones. You can see my "Vacuum Tube Battery Box" power supply right below the receiver.

​Step 8 Testing

I am using a crystal earphone for testing. A crystal earphone looks like an "open" to DC current. A 47K resistor needs to soldered accross the Phones terminals for the crystal earphone to work.

Set the Tuning, Detector, Filament, and Regeneration controls to mid position. You should hear atmospheric "hiss" from the earphone, once the power supply, antenna, and ground are connected. Use the Tuning knob to select AM broadcasts. Once selected, adjust the Regeneration control counter-clockwise to the point of where you hear oscillation or "squeal", then turn it clockwise slightly until the oscillation stops and the AM broadcast is clear. Use the Detector control to "peak" the signal.

​Turn the Regeneration control further clockwise to reduce receiver gain if the AM broadcast is overpowering the earphone. The only time you should need to adjust the Filament control is if your A+ batteries are getting weak. Adjust the control until there is 2 Volts at the filament pins of the Type 30 and Type 32 vacuum tubes.

​Troubleshooting

Here are some troubleshooting tips if your regenerative receiver is not working as expected.

No sound from earphone:

Check wiring with power source disconnected.

Connect power source, check Voltages at the power terminals of the receiver to make sure they are correct.

Turn out the lights and make sure the filaments of the Type 30 and Type 32 tubes are glowing.

If using a crystal type headset or earpiece to listen, attached a 47K 1/4 Watt resistor across the Phones leads to ensure the proper current flow.

Make sure you have high Impedance headphones connected to your receiver. The Impedance must be at least 5K, common 8ohm headphones will not work.

AM Broadcast are weak, Regeneration control does not have any effect:

Switch the two Type 30 Vacuum tubes, I found that one tube worked better as a RF Amplifier/Detector while the other Type 30 Vacuum tube work better as an Audio Amplifier. Remember, these vacuum tubes are over 85 years old!​

​Conclusion

This was a most gratifying project. When not in use it is proudly displayed on a shelf in my basement "Man Cave". Building a Doerle "Signal Gripper" Regenerative Shortwave Receiver is a great way to learn about electronics past.

What is an IF Transformer?

An IF, or Intermediate Frequency, transformer is a tuned air core transformer used in just about all analog Superheterodyne receivers in past and current AM and FM designs. Most Superheterodyne receivers have two or more IF Transformers to increase signal gain and selectivity. Selectivity is the ability of a radio receiver to focus on one broadcast while rejecting others that are close in frequency as the desired one.

Superheterodyne radios take an incoming broadcast and convert it to an intermediate frequency using a process called Heterodyning. IF Frequencies have been standardized on the broadcast bands with 455Khz used for AM and 10.7Mhz used for FM. Heterodyning is used as it is more efficient and cost effective to design an RF amplifier for a small window of frequencies than to design one efficient across and entire broadcast band. Circled below is the case of a typical IF Transformer. It is mounted to the chassis using two clips. One can be seen in the picture below.

How can I tell if one is bad?

This blog is dedicated solely to the IF Transformers used in vintage radios that employ electron tubes and not transistor designs. The IF Transformers used in transistor radio designs are typically too small to service and there is still a ready supply available, making it more cost and time effective to just replace.

Like common power transformers, an IF Transformer has a primary and a secondary winding. The difference between power and IF Transformer is:

Power transformers typically have a different number of turns between primary and secondary windings, thereby, increasing or decreasing the voltage and current amplitude across the secondary winding. IF Transformers typically have a 1:1 ratio where the number of turns on the primary and secondary winding are equal.

Power transformers operate at low frequencies, typically between 60 and 120 Hz and require heavy steel laminated core to concentrate the lines of magnetic force into the secondary windings. IF Transformers, due to their high operating frequency, can work efficiently with an "air" core which is no core at all, just a cardboard form to hold the primary and secondary winding in place.

The easiest way to check if an IF Transformer is OK is my measuring the DC resistance of the windings. There should be a very low resistance (typically less than 50 Ohms) between the lead wires connected to each winding.

While it is best to try to completely remove the IF Transformer from the circuit to test the winding resistance, if you consult the schematic of your vintage radio, you may find you can isolate the winding from the circuit to test by simply removing the electron tube connected to the winding.

Using an Ohmmeter and testing the resistance with the electron tube removed, I had determine that the secondary winding in the Second IF Transformer had an "open" or broken connection.

​"Old Time Radios! Restoration and Repair" book on Amazon

I consult this book often during radio restoration. I grew up in the transistor and rectifier era and this book taught me a lot about vacuum tube and selium rectifier technology.

Repairing a Vintage IF Transformer

The only time I would recommend repairing a vintage IF Transformer is when a replacement one is not readily available available in your junk box.

Step 1 Removing the IF Transformer from the Radio Chassis:

First, document the IF Transformer's connections so you know how to reconnect it into the circuit. The IF Transformer's connections enter the bottom of the chassis through four holes, circled in the picture below. Next, desolder the IF Transformers connections. The insulation on several wires has crumbled to the touch. I will either have to replace those wires or use heat shrink tubing to insulate.

An IF Transformer is typically enclosed in an aluminum case. There are tabs on the case that attach if to the radio's chassis through slots. The tabs are bent so as to prevent them from coming out of the chassis slot. The IF Transformer's tabs are sometimes soldered to the chassis. Regardless, the IF Transformer case tabs must be freed.

Below is the typical "guts" of a vintage IF Transformer. In this picture the IF Transformer leads have already been removed. The leads are to be replaced as the wire insulation became brittle and has fallen off. The two rings on the cardboard form are the primary and secondary windings wound in "Universal", fashion, which achieves both high inductance and Q in a very small space. The wire used in the winding is of a special type called Litzendraht, or Litz wire for short. Litz wire consists of many thin wire strands, individually insulated and twisted or woven together, following a carefully prescribed pattern. Litz wire reduces what is know as "Skin Effect" and better conducts alternating current at high frequencies.

The primary and secondary winding leads connect to terminals on the white ceramic block at the top. This ceramic block contains two compression type trimmer capacitors. One is connected in parallel to the primary winding and the other in parallel across the secondary winding. The capacitance can be varied between 75 to 160 pf by a screw on top. The screw compresses two metal plates against a mica insulator and the capacitance is varied based on the the screw tightness. In addition, the white ceramic block contains a fixed 120pf capacitor with separate leads that needs to be wired into the radio's circuit.

Step 2 Calculations:

Two calculations need to be performed before winding the new coil. First, we need to determine the required Inductance of the coil. Then, the number of turns required will need to be calculated in order to achieve the required Inductance.

We need the new coil to be wound so that it has the proper Inductance to achieve resonance at 455Khz, when wired in parallel with the trimmer capacitor located at the top of the IF Transformer. As mentioned, 455Khz is the IF Frequency used in standard AM broadcast band receivers.

To the resonant frequency, the parallel capacitor and Inductor will provide a high impedance, all other frequencies it will act as a very low impedance or a short. Only the resonant frequency will be passed to the following detector stage.

The trimmer capacitor can be varied between 75pf and 160pf, so we use the mean value of 117.5pf for Capacitance. Using the Online Tank Circuit Resonance Calculator listed below, and by plugging in 117.5p (pf) as the Capacitance and 1m (mH) as Inductance, you can see that the resonant frequency is 0.4643 MHz or 464.3 kHz. This is close to the required 455 kHz resonance frequency required. If we plug in 75p (pf) as Capacitance with a 1m (mH) Inductor the resonant frequency changes to .5812 MHz or 581.2 kHz. In addition, if we plug in 160p (pf) as Capacitance with a 1m (mH) Inductor the resonant frequency changes to .3979 MHz or 397.9 kHz. This indicates that we can adjust the trimmer capacitor between the values to 75pf and 160pf and be able to achieve resonance at 455kHz.

OK, so we have determined the coil to be wound should provide an Inductance of 1mH. Next we need to determine how many turns of magnet wire are required to achieve this goal. I plugged the following values into the ONLINE MULTILAYER AIR CORE INDUCTOR CALCULATOR, listed below:
Inductance: 1mH
Coil Inner Diameter: .25 inches
Coil Length: .5 inches
Wire Gauge: 26AWG
The online calculator returns the Number of Turns (N) to be 375. Now we have all the required information to wind the new Secondary IF Transformer winding.

Step 3 Creating a new Secondary IF Transformer Winding:

In my case, the secondary winding located toward the bottom of the IF Transformer had an open in it and needed to be replaced. I unsoldered both the primary and secondary winding leads from the white ceramic block containing the trimmer capacitors then detached the cardboard tube so as to make it easier to handle. I then used wire cutters to cut through the defective secondary winding in order to remove it. See the results below:

I will not be replacing the defective secondary winding using Litz wire wound in a Universal pattern. This requires a special winding tool that I do not possess. Instead, I will create a spool towards the bottom of the cardboard form and wind multiple layers of 26 AWG magnet wire to achieve the same results. I fashioned the ends of the spool from two plastic bottom caps. See below:

I then used SuperGlue to attach the spool ends to the cardboard form. The distance between the spools ends is a 1/2 inch. The spool is centered at the location of the old secondary winding.

Based on my calculations, 375 Turns of 26 AWG magnet wire needed to be wound on the homemade spool. I used a tiny drill and drilled a hole at the base of the spool on the bottom end. I then threaded the wire through it so that 4 inches was exposed, this is to be one lead of the coil. I then wound as many turns and I could fit across the spool placing a piece of masking tape over the layer when done. The next layer was wound in the opposite direction. Below is a picture of my first winding layer covered in masking tape.

Below is a picture of the completed new secondary winding. I drilled a second small hole then threaded the wire through it to make the second coil lead.

The next step was to cut the leads of the new secondary winding to the proper length.

I then used an X-Acto knife to scrap off the varnish on about 1/8 inch from the end of each lead exposing the copper. The next step was to solder one coil lead to a terminal of a trimmer capacitor.

I added a 22 Ohm resistor in series with the other lead, in order to get the desired DC resistance of the Litz wire winding I was replacing. The other end of the resistor was soldered to the other terminal of the same trimmer capacitor.

I also had to solder the leads of the primary winding to the second trimmer capacitor.

As mentioned, all of the insulation on the leads of the IF Transformer had rotted and cracked off, leaving exposed wire. I replaced the IF Transformer leads with "Bell Wire" soldered to the trimmer and fixed capacitor's terminals.

Below is a picture of the finished product:

The next step is to stuff the IF Transformer "guts" back into the aluminum case. Make sure that the Fishpaper that insulates the aluminum case is still in place. Also make sure the trimmer capacitor adjustment screws can be accessed from the top of the aluminum case. The last step is to install the brass retainer strip that centers the transformer assembly in the case. See below:

Step 4 Testing and Initial Alignment:

I connected the primary winding of the repaired IF Transformer to my Eico RF Signal Generator. I then set the RF Generator to an unmodulated .02 Volts Peek to Peak 455kHz signal. The secondary winding was connected to my Oscilloscope. I then proceeded to adjust the screw of each trimmer capacitor, with a non-metallic alignment tool, for maximum amplitude on the scope.

Step 5 Install repaired IF Transformer into Radio Chassis:

The next step is to install the repaired IF Transformer back into the radio chassis. Here is a picture of the wiring from the bottom. I have circled the openings where the IF Transformer leads enter the chassis. You will notice a total of six wires. The Yellow and Black leads connect to the Primary IF Transformer winding while the Purple and White leads connect to the Secondary winding. The two additional red/white striped wires connect to a fixed value 120pf capacitor built into the same ceramic block that also houses the IF Transformer's trimmer capacitors.

Step 6 Final Testing:

Time to power up the chassis and see if the repaired IF Transformer works correctly in the actual circuit. Success! I could immediately start to hear broadcast stations once the electron tubes warmed up. In order to perform final adjustments, I picked a broadcast station in the center of the tuning dial then adjusted the trimmer capacitor's adjustment screw, one at a time on both IF Transformers, for maximum station volume. Below is a video of the initial power up of my RCA 15X AM Radio with a repaired IF Transformer.

Conclusion

This blog instructs you on how to repair a type of IF Transformer typically used in vintage tube radios. I would only recommend repairing an IF Transformer if one was not immediately available or if the IF Transformer was specialized and a suitable replacement could not be found. Repairing an IF Transformer is a good way to save an old radio from the scrap heap.

About the Messenger 1

The Messenger 1 was a radio transceiver, designed by the EF Johnson company, for two-way radio service in the 27Mhz Citizens band. This transceiver was manufactured beginning in 1958 until the early 1960s. In 1961 it went for around 140 dollars retail. The Messenger 1 consists of a crystal controlled Superhet receiver and a crystal controlled two-stage transmitter. The antenna, power supply, and some of the audio circuits are shared between receiver and transmitter functions.

There are five different models, each with different operating voltages. My Messenger 1 is a model 242-128 that can be powered by 12 Volts DC for mobile, or 117 Volts AC for base station use. For 12 Volt DC operation, the Messenger 1 uses a vibrator relay to pulse the current through a step up transformer in order to achieve the high B+ Voltage required for the electron tubes.

The Messenger 1 has a complement of ten electron tubes and 2 diodes. Its crystal controlled frequency range is between 26.965 to 27.555 Mhz incremented into five channels.

It dimensions are 5 5/8 Inches high, 7 Inches wide and 11 3/8 Inches deep which is quite bigger than the transistorized CB radios of the 1970s. In addition it weighs a fairly hefty 12 pounds!

About the EF Johnson Company

EF Johnson, started in 1923, is a Waseca Minnesota based two-way radio manufacturer founded by Edgar. F. Johnson. It started as a mail order business, selling radio transmitter parts to amateurs and early radio broadcasters.

Like many American companies, its production was devoted to the war time effort during World War II. After the war, the company introduced its Viking line of amateur transmitters, among them, the Viking, Valiant, Ranger, and Pacemaker. The now discontinued Viking line of amateur radio transmitter products are collected, restored, and operated by many vintage radio enthusiasts.

In 1961 the company transitioned to the development and manufacturing of land-mobile radio products such as CB, business radio, and associated technology such as the Logic Trunked Radio trunking format.

The EF Johnson Company, now rebranded EFJohnson Technologies, has completely left the consumer market and focuses mainly on radio equipment used law enforcement, firefighters, EMS, and military.

Below is a picture of the of the Messenger 1 microphone with push to talk button. The high impedance ceramic microphone element is housed in a Cycolac case.

Pictured below is the back of the Messenger 1, on the bottom left is the power connector. On the right hand side is the antenna connection. You can see the base of the vibrator relay, used in the high voltage power supply circuit when powered by 12 Volts DC, through the hole.

The EF Johnson Viking emblem, I plan on cleaning it up then applying red enamel paint to the "J" and black enamel to the background around the Viking.

The inside of this Messenger 1 is pretty nasty, several of the electron tubes were missing and one was cracked and unusable. I found a petrified hornets nest inside the underside of the chassis. Still there is promise. You can see towards the bottom where I wiped the chassis with a Windex moistened paper towel. Somewhere under all of this dirt is a working CB transceiver!

Conclusion

Stay tuned and visit radioboatanchor.com often to see updates of the Messenger 1 restore and many other projects!